Foam Template Research Articles

Thermal gelation of cellulose based suspensions

A more sustainable future calls for bio-based alternatives to replace plastic foams for various applications, such as packaging, insulation and cushioning. Some bio-based foams emerging in scientific publications are fabricated using liquid foam templating and methyl cellulose as well as fibers as main constituents. Scaling up of the production, however, requires a comprehensive understanding of the rheology of the foam during the shaping and drying processes. In this article, we report rheological studies of cellulose based systems in the context of thermal gelation. In more precise terms, we study how the presence of cellulose fibers and other additive materials influences the thermal gelation properties of methyl cellulose. We observe that the rheological properties, while heavily dependent on the material composition, are reasonably adjustable by appropriate material choices. The fibers are seen to decrease the temperature required for methyl cellulose to undergo a viscoelastic transition which is useful in the solid foam fabrication process. We anticipate that in the present application, the fibers increase the stability of the desired structure during the drying stage of the foam.

Three‐dimensional graphene/carbon nanotube electromagnetic shielding composite material based on melamine resin foam template

AbstractElectromagnetic shielding materials with good ductility, low density, and high shielding performance have excellent application prospects in communication and electronics, aerospace, and military industry. Lightweight three‐dimensional porous conductive foam composite with high electrical conductivity and electromagnetic shielding efficiency has been widely concerned in recent years. In this study, we prepared a special physically modified carbonized melamine foam (CMF) by synergistic modification with graphene (GNs) and multi‐walled carbon nanotubes (CNTs). The lightweight CMF composite with a Unique 3D pore structure has been constructed to achieve high efficiency in EMI shielding. Taking advantage of the synergistic effect of few‐layer nanosheets and CNTs in tailored microporous structure, 15 wt% GNs‐CNTs/CMF composite demonstrates low density of 0.03 g/cm3 and high electrical conductivity of 34.0 S/m, resulting in a significant EMI shielding effectiveness as 3840 dB⋅cm2/g. The microporous architecture contributes to multiple reflection losses of electromagnetic waves by introducing multiple interfaces and also improves the construction of conductive paths to deliver outstanding shielding performance. This work illustrates reference significance for the potential application of lightweight EMI shielding materials with target functions.

SiC Foams for the Photocatalytic Degradation of Methylene Blue under Visible Light Irradiation.

SiC foams were synthesized by impregnating preceramic polymer into polyurethane foam templates, resulting in a photo-catalytically active material for the degradation of methylene blue. The crystalline structure, electronic properties, and photocatalytic performance of the SiC foams were characterized using a series of experimental techniques, including X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, N2 physisorption measurements, UV-visible spectroscopy, and methylene blue photodegradation tests. The original polyurethane template's microporous structure was maintained during the formation of the SiC foam, while additional mesopores were introduced by the porogen moieties added to the preceramic polymers. The prepared SiC-based photocatalyst showed attractive photocatalytic activity under visible light irradiation. This structured and reactive material offers good potential for application as a catalytic contactor or membrane reactor for the semi-continuous treatment of contaminated waste waters in ambient conditions.

Hierarchical Porous Monoliths of Steel with Self-Reinforcing Adaptive Properties.

Porous structures offer an attractive approach to reduce the amount of natural resources used while maintaining relatively high mechanical efficiency. However, for some applications the drop in mechanical properties resulting from the introduction of porosity is too high, which has limited the broader utilization of porous materials in industry. Here, it is shown that steel monoliths can be designed to display high mechanical efficiency and reversible self-reinforcing properties when made with porous architectures with up to three hierarchical levels. Ultralight steel structures that can float on water and autonomously adapt their stiffness are manufactured by the thermal reduction and sintering of 3D printed foam templates. Using distinct mechanical testing techniques, image analysis, and finite element simulations, the mechanisms leading to the high mechanical efficiency and self-stiffening ability of the hierarchical porous monoliths are studied. The design and fabrication of mechanically stable porous monoliths using iron as a widely available natural resource is expected to contribute to the future development of functional materials with a more sustainable footprint.

Porous materials prepared from eco-friendly attapulgite and gallnut stabilized aqueous foam templates for high-efficient removal of organic pollutants

To date, whether it is the fabrication or adsorption process or the regeneration of adsorbent materials, cleanliness and environmental friendliness have been pursued by researchers. Herein, a novel and eco-friendly porous material was fabricated via the Pickering aqueous foam and applied to remove organic pollutants of brilliant green and chlortetracycline. The Pickering foam showed excellent stability and was synergistically stabilized by natural nanomaterials—attapulgite and botany—gallnut. The characterization result revealed that the attapulgite was modified by the organic molecular leached from the gallnut, and then adsorbed and formed a rigid shell at the water-air interface to prevent the coalescence and drainage of the bubble. The as-prepared porous adsorbent possessed excellent adsorption capacities of 939.83 and 465.85 mg/g for brilliant green and chlortetracycline and could be utilized cyclically at least 10 times by the carbonization regeneration at 400 °C under N2 atmosphere. Overall, this work provided a sustainable and eco-friendly approach to fabricate porous material, and the material might have huge potential in practical applications as it has the excellent adsorption performance and the reusability.

Shortening replacement by emulsion and foam template hydroxypropyl methylcellulose (HPMC)-based oleogels in puff pastry dough. Rheological and texture properties

Shortening plays an essential function in the formulation of sweet laminated bakery products, but has a potential health risk due to their high percentage of saturated fatty acids. In this paper, the feasibility of hydroxypropyl methylcellulose (HPMC) oleogels prepared with emulsion template (ET) and foam template (FT) approaches as fat sources in a puff pastry dough was investigated. Spreadability and thermal properties of control shortening, 100% ET and FT oleogels and shortening/oleogel (50/50) blends were measured. The different systems were applied as the fat source in a puff pastry dough, and their effect on rheological and texture properties was investigated. Results showed that partial replacement of shortening with oleogels could significantly decrease the firmness values (from 115 to 26 N) (P < 0.05) and increased the spreadability of shortening. The methodology to prepare the oleogel (FT or ET) also significantly affected the texture parameters. FT blends had the highest spreadability with significantly lower firmness values and area under the curve. Thermal values showed that both oleogels could slightly increase the melting point of shortening from 47 to 50 °C. The replacement of shortening with oleogel decreases the viscoelasticity of puff pastry dough and increases its thermal stability but does not significantly change dough viscoelasticity in the shortening/oleogel mixture. These results indicated that both oleogels have promising potential to replace shortening in puff pastry dough formulations, but the ET oleogel showed a more similar behavior to the control shortening than the FT oleogel.

Comparison of different indirect approaches to design edible oleogels based on cellulose ethers

Growing public concern about the adverse health effects of overconsumption of saturated fat has contributed to the rising research interest in the field of using healthy oils to construct edible structured oils (oloegels) as fat-based alternatives. In this study two indirect methodologies (the emulsion template approach and the foam template approach) were investigated to prepare oleogels with hydroxypropyl methylcellulose and methylcellulose as gelling agent at three different oil concentrations. Microstructure, texture, rheology, and oil retention capacity were measured to evaluate the structural and physicochemical properties of oleogels. Results showed that the emulsion-based oleogel effectively inhibited the aggregation of droplets. The dry emulsion showed independent droplets and an oil retention capacity of 100%. In foam-type oleogels the oil retention rate was negatively correlated with the oil content. The oleogels prepared by both methods have excellent mechanical properties and gel strength, with a predominance of the elastic versus the viscous behavior. Hydroxypropyl methylcellulose and methylcellulose had different degrees of influence on the structure and mechanical properties of the two oleogels. The results of this paper provide guidance for the development and application of cellulose-based oleogels as healthy alternatives to saturated fat. • Different approaches result in different microstructure and oil retention capacity. • Oil content plays an important role in textural and rheological properties. • Oleogels present high gel strength and low dependence on frequency and temperature.

A better picker-upper: Superabsorbent “gel sheets” with fabric-like flexibility

<h2>Summary</h2> Materials to absorb aqueous liquids are either foldable cloth/paper towels (convenient to use but poorly absorbent), or superabsorbent polymer hydrogels (highly absorbent, but fragile when dried). Here, we create "gel sheets" that combine the best attributes from the above. Macrosized sheets (10 × 10 cm) are prepared by foam templating, followed by plasticization and ambient drying. The dried sheets are macroporous, flexible, soft, and robust; they can be folded, rolled up, and cut with scissors, much like fabrics. At the same time, like hydrogels, they substantially absorb water and <i>expand as they absorb</i>, which is unlike any sponges or towels. The sheets also absorb viscous liquids like blood and viscoelastic liquids like polymer solutions. Absorbed liquid is retained within the sheet when lifted, whereas excess liquid drips from towels. Such gel sheets could be used to clean up spills in homes, labs, and hospitals, and for absorbing biological fluids during surgeries.

Fabrication of porous adsorbents from eco-friendly aqueous foam for high-efficient removal of cationic dyes and sustainable utilization assessment

Porous materials applied in environmental remediation have received researchers’ extensive attention recently, but the related green and convenient preparation method is rarely reported. Here, we recommended a green and convenient strategy for the fabrication of porous material via aqueous foam templates, which was synergistically stabilized by Codonopsis pilosula (CP) and clay minerals of attapulgite (APT). The characterization results revealed that the APT was modified by organic molecules leached from CP and anchored at the air-water interface, which improved the foam stability significantly. The novel porous material of polyacrylamide/Codonopsis pilosula/attapulgite (PAM/CP/APT) templated from the aqueous foam via a polymerization reaction had excellent adsorption capacity for the cationic dyes methyl violet (MV) and methylene blue (MB), and the adsorption capacity can reach 755.85 mg/g and 557.64 mg/g, respectively. More importantly, the adsorption capacity of spent adsorbent material was still over 200 mg/g after being recycled five times through a simple carbonization process, and then it was added to the plant pot, the total biomass was increased by about 86.42%. This study provided a green and sustainable pathway for the preparation, application and subsequent processing of porous materials.

Thermal insulating and fire-retardant lightweight carbon-slag composite foams towards absorption dominated electromagnetic interference shielding

Herein, we developed a simple and feasible strategy to introduce blast furnace slag (SL) an industrial waste into phenolic resin, and then synthesized a lightweight and thermal insulating carbon-slag composite foam via polyurethane (PU) foam template method followed by carbonization at 1000 °C. The electromagnetic interference (EMI) shielding effectiveness (SE) and complex permittivity and permeability of carbon-slag composite foams were measured in the X band (8.2–12.4 GHz) frequency range. A maximum EMI shielding of 48.9 dB was achieved for carbon foam (CF) with 20% slag inclusions (CF-20SL) at only 2 mm thickness. It can be extensively seen that the absorption of CF-20SL was increased by 3 times compared with neat CF. The improved absorption can be attributed to high dielectric and magnetic losses and interfacial polarization in carbon-slag composite foams. Moreover, the synergistic effect of carbon and slag not only increases the EMI shielding properties but also enhances the thermal insulation, thermal stability, and flame retardancy of carbon-slag composites foam. The resultant composites foam (CF-20SL) exhibited the lowest thermal conductivity of 0.08 W/m.K and excellent thermal stability up to 500 °C in an oxidative environment. All the results indicated that such kind of carbon-slag composite foam is expected to be used in next-generation lightweight EMI shielding and thermal insulating material in defense and aerospace applications.

Colloidal co‐assembly of dual‐phased ceramic/metal particles toward lightweight, hierarchically structured, and mechanically robust alumina foam

AbstractCeramic foams constructed by aqueous‐based foam templating have demonstrated great potential in industrial and research applications. However, a multiple‐phased suspension with inherently improved complexity inevitably leads to a severe deterioration of foam stability. Herein, we proposed a colloidal co‐assembly strategy that introduces Al–Al2O3 dual‐phased particles for constructing ultralight yet mechanically robust cellular ceramics. Owing to the Al2O3 oxidation layer on Al particles, both of Al and Al2O3 suspensions demonstrated similar zeta potential and rheological properties, enabling a stable foam structure after colloidal co‐assembly. High‐temperature oxidation of Al particles contributed to the reinforcement of cell wall and formation of Al2O3 whiskers. The calcined products demonstrated a lightweight structure (0.31 g cm−3), a robust compressive strength (3.64 MPa) at a porosity level of 88.5%, and a relatively high specific surface area (14.7 m2 g−1). The current strategy paves the way for the construction of high‐performance ceramic foams for a broad range of applications.

Comparison of Hydroxyapatite/Poly(lactide-co-glycolide) and Hydroxyapatite/Polyethyleneimine Composite Scaffolds in Bone Regeneration of Swine Mandibular Critical Size Defects: In Vivo Study.

Reconstruction of jaw bone defects present a significant problem because of specific aesthetic and functional requirements. Although widely used, the transplantation of standard autograft and allograft materials is still associated with significant constraints. Composite scaffolds, combining advantages of biodegradable polymers with bioceramics, have potential to overcome limitations of standard grafts. Polyethyleneimine could be an interesting novel biocompatible polymer for scaffold construction due to its biocompatibility and chemical structure. To date, there have been no in vivo studies assessing biological properties of hydroxyapatite bioceramics scaffold modified with polyethyleneimine. The aim of this study was to evaluate in vivo effects of composite scaffolds of hydroxyapatite ceramics and poly(lactide-co-glycolide) and novel polyethyleneimine on bone repair in swine’s mandibular defects, and to compare them to conventional bone allograft (BioOss). Scaffolds were prepared using the method of polymer foam template in three steps. Pigs, 3 months old, were used and defects were made in the canine, premolar, and molar area of their mandibles. Four months following the surgical procedure, the bone was analyzed using radiological, histological, and gene expression techniques. Hydroxyapatite ceramics/polyethyleneimine composite scaffold demonstrated improved biological behavior compared to conventional allograft in treatment of swine’s mandibular defects, in terms of bone density and bone tissue histological characteristics.

Porous materials fabricated from Pickering foams stabilized by natural plant of Angelica sinensis for removal of Cd (II) and Cu (II)

The emulsion or foam templating applied in the preparation of porous materials have been widely studied. As the enhancement of the green and environmental protection awareness in preparation process, the stabilization of the emulsion or foam with the natural matter has been attracted extensive attention. In this work, a high stable Pickering water-based foams was stabilized by the natural plant Angelica sinensis, and a novel porous material of Polyacrylic acid-Angelica sinensis (PAA-AS) was fabricated from the Pickering foam via a thermally-initiated polymerization. Duo to the amphiphilic organic molecules was rich in AS, such as phenolic acids, saponins, etc., the water-based foam can be stabilized by the AS particles alone. The as-prepared porous materials had sufficient pore structure, and the pore size could be controlled by changing the dosage of AS. PAA-AS was applied to remove heavy metal ions from water, and the adsorption capacities for Cd2+ and Cu2+ could be reached to 372.74 mg/g and 186.83 mg/g, respectively. In brief, this research provided a new approach to prepare environmentally friendly porous materials, and the materials has the applications potential in water treatment.

Bimetallic nanoarrays embedded in three-dimensional carbon foam as lightweight and efficient microwave absorbers

The rapid development of electronic information technology has promoted the use of a large number of high-frequency electronic equipment, which has led to increasingly serious electromagnetic interference (EMI) problems caused by disordered radiation. At present, for the 2–18 GHz microwave frequency band, it is still a huge challenge to develop high-efficiency absorbing materials with ultra-wide absorption band (>7 GHz) under thin thickness (<3 mm). Here, we propose a new strategy to achieve lightweight and high-efficiency microwave absorption by constructing hierarchical special structures. The melamine foam template was coated with a carbon/nickel/cobalt organic precursor by a hydrothermal process using a water/ethanol mixed solvent, and then annealed in an inert atmosphere at a high temperature to obtain a bimetallic nanoarray composed of nickel/cobalt embedded three-dimensional carbon foam (BNA/3dCF). This new type of absorbing material completely retains the structure of the melamine foam template, greatly enhances the conduction ability of micro-currents, and provides a large number of scattering sites for electromagnetic wave conduction. Interestingly, the protection of the carbon layer effectively avoids the oxidation of the bimetallic nanoarray, so that the BNA/3dCF retains the good dielectric properties of the carbon foam and has excellent magnetic properties, and improves the impedance matching and magnetic loss capabilities. With matching thicknesses of 2.2 mm and 3.9 mm, BNA/3dCF can respectively obtain an ultra-wideband microwave absorption of 7.16 GHz and a minimum reflection loss of −57.84 dB. We believe that through the macro/meso/micro multi-scale precise control of the absorbing material, it is an effective solution to enhance its absorbing performance.

Формирование биомиметического апатита на кальцийфосфатной пенокерамике в концентрированной модельной среде

By firing polyurethane foam templates (“STR” brand, 12 pores per cm, China) with a porosity of ~ 65 % at 1200 °С, an open-pore calcium phosphate foam ceramics was obtained using a highly concentrated suspension based on synthetic hydroxyapatite, heat-treated at 800 °С, monocalcium phosphate monohydrate and 0.8 % polyvinyl alcohol. The resulting calcium phosphate foam ceramics after modification in the SBF (Simulated Body Fluid) solution concentrated 5 times (SBF×5) consisted of β-tricalcium phosphate, β-calcium pyrophosphate and biomimetic apatite, had a porosity of 53 – 59 % and a static strength of ~ 0.05 MPa. The formed biomimetic apatite, consisting of amorphous calcium phosphate Ca9(PO4)6 and apatite tricalcium phosphate Ca9HPO4(PO4)5OH, crystallizes into β-tricalcium phosphate at 1200 °С. Calcium phosphate foam ceramics modified with biomimetic apatite, after soaking in 5 % hydroxyapatite gel and SBF×5, which simulating a bone defect in vitro, in parallel with the formation of biomimetic apatite, is partially destroyed, which confirmed its high bioactivity and degradation.

Facile fabrication of the porous adsorbent from natural plant Angelica Sinensis stabilized liquid foam for dye removal

Porous materials as emerging high-efficiency adsorbents have attracted increasing attention in recent years, due to the high specific surface area, fast adsorption rate, favorable adsorption capacity to heavy metal, dyes, and other pollutants, etc. Among various approaches, the foam template method with the advantage of flexible operation and controllable pores structure is proposed to prepare net type of porous adsorbents with superior adsorption capacity and rapid adsorption rate. In this process, natural plant Angelica Sinensis (AS) was treated with a simple alkaline-heat process, and the resultant product was used firstly to prepare foam with high stability, and the positive effect of the cellulose dissociation and the conversion of ligustilide into amphiphilic moleculars on improving the stability of Pickering foam was revealed. The liquid foam can serve as pore-foaming template and precursor of polymerization for synthesizing porous adsorbent by one-step integrated process of free radical polymerization and silane hydrolysis. The porous adsorbent showed the sufficient porous structure and excellent adsorption performance for cationic dye, with maximum adsorption capacities of 386.13 mg g-1 and 284.20 mg g-1 for methyl violet (MV) and malachite green (MG). In a word, the novel approach can provide an important reference for green synthesis of high stable foam and the superporous material, and the adsorbent showed great application potential in the field of water treatment.

Harnessing Ostwald ripening to fabricate hierarchically structured mullite-based cellular architecture via the gelation network-triggered morphology-regulation method

Gas-in-liquid foam templating is considered as a promising method for commercial-scale production of porous materials. However, Ostwald ripening occurs frequently during the preparation, which could bring about inhomogeneous bubbles with large sizes and deteriorate the performance of resultant products. To tackle this challenging task, we report a gelation network-triggered morphology-regulation strategy during the foaming process. As an exemplar, boehmite sol was incorporated into the andalusite suspension to stabilize the foam framework. After casting, the wet foam was able to maintain its overall shape, since andalusite particles were anchored onto the gas-liquid interface by the gelation network during mechanical frothing. The samples calcined at 1400°C feature homogeneous bubble with hierarchical porous architecture, smaller pore size with a mean value of 5.32 μm and robust compressive strength of 11.97MPa at a porosity level of 84 %. Our approach substantially broadens the design philosophy of high performance porous ceramics.

Highly Sensitive Capacitive Pressure Sensors over a Wide Pressure Range Enabled by the Hybrid Responses of a Highly Porous Nanocomposite.

Past research aimed at increasing the sensitivity of capacitive pressure sensors has mostly focused on developing dielectric layers with surface/porous structures or higher dielectric constants. However, such strategies have only been effective in improving sensitivities at low pressure ranges (e.g., up to 3kPa). To overcome this well-known obstacle, herein, a flexible hybrid-response pressure sensor (HRPS) composed of an electrically conductive porous nanocomposite (PNC) laminated with an ultrathin dielectric layer is devised. Using a nickel foam template, the PNC is fabricated with carbon nanotubes (CNTs)-doped Ecoflex to be 86% porous and electrically conductive. The PNC exhibits hybrid piezoresistive and piezocapacitive responses, resulting in significantly enhanced sensitivities (i.e., more than 400%) over wide pressure ranges, from 3.13 kPa-1 within 0-1 kPa to 0.43 kPa-1 within 30-50 kPa. The effect of the hybrid responses is differentiated from the effect of porosity or high dielectric constants by comparing the HRPS with its purely piezocapacitive counterparts. Fundamental understanding of the HRPS and the prediction of optimal CNT doping are achieved through simplified analytical models. The HRPS is able to measure pressures from as subtle as the temporal arterial pulse to as large as footsteps.

Investigation of a Template‐Based Process Chain for Investment Casting of Open‐Cell Metal Foams

Herein, a holistic investigation of the process chain of polymer foam template manufacturing for the investment casting of open‐cell metal foams and their evaluation in terms of mechanical response under compressive loading is presented. Polymer foam templates are manufactured using sucrose beads as spaceholders with a body‐centred cubic (bcc) stacking and epoxy resin as matrix material. These templates are used in a modified investment casting process to produce commercial pure open‐cell Al foams (AA 1050 A). The materials used for the polymer foam templates are suitable for the template production and the use in investment casting. The structure of the template can be exactly reproduced by investment casting and no byproducts from the pyrolysis step can be detected within the molds or the Al foams. The mechanical properties under compressive loading are comparable with high‐strength Al‐alloy foams with a structure factor of C1 of 0.60. The characteristic plastic deformation is dominated by buckling, showing a local plastic failure of the struts within cell layers. Due to a high node‐to‐strut thickness ratio, neither small defects in the microstructure nor stacking errors of the template impact this deformation behavior.

Rapid Prototyping of Carbon‐Bonded Alumina Filters with Flame‐Sprayed Alumina Coating for Bottom‐Teeming Steel Ingot Casting

Although continuous casting is the state‐of‐the‐art casting method in steelmaking, ingot casting by bottom teeming has kept its relevance, for example, in the area of specialty steels. The main challenge is to meet the ever‐increasing quality requirements demanded by the customers. Regarding high‐performance steel applications, the purity with respect to the content of nonmetallic inclusions thereby is of special interest. Herein, foam templates with tailored geometry are designed and manufactured by selective laser sintering. Different coating techniques based on carbon‐bonded alumina slurries are applied to replicate foam structures with miniature cube geometry and cylindrical geometry. The techniques are evaluated regarding the porosity, pore size distribution, bulk density, mechanical strength, and shrinkage of the resulting filters. Suitable processing routes are selected to manufacture prototype batches with near‐net‐shape geometry. Finally, the feasibility of applying a flame spray coating is tested. First samples of the prototype batch are tested in industrial bottom‐teeming ingot casting.